In the manufacture of printed circuit cards and boards, a dielectric sheet material is employed as the substrate. A conductive circuit pattern is provided on one or both of the major surfaces of the substrate.
In order to provide an electrical connection between layers, metal coated vias are provided. In providing a connection of conductive patterns through a dielectric material, to a large extent, a conductive land and line are provided on the surface of the dielectric material. However, the presence of a land is undesirable on the dielectric material since it takes up valuable area on the dielectric material which could be used for other purposes.
For instance, certain techniques have been suggested for providing landless through-hole connections. Such techniques include those suggested by Crimi, et al. in IBM Technical Disclosure Bulletin, Volume 9, No. 10, March 1967; Mead, IBM, Technical Disclosure Bulletin, Volume 13, No. 1, June 1970; Chumbres, et al., IBM Technical Disclosure Bulletin, Volume 15, No. 10, March 1973; and U.S. Pat. No. 4,704,791 to Chellis, et al. However, for those circuit boards and cards that have internal signal planes, it is desirable to provide electrical connection between an external layer and an adjacent internal signal layer through the use of a blind via. Blind vias are advantageous since the number of inner connections can be doubled compared to employing through holes or vias. In particular, blind vias can be applied to both sides of the circuit board or card at the suitable site.
Furthermore, the current surface geometry for a solder ball connection (SBC) or flip chip attachment (FCA) requires a "dogbone" pattern wherein one end is used for the SBC mount and the other end is used to contain the via for signal distribution. Mounting the substrate such that the solder ball is directly on the via site is not possible in such configurations since the solder must be constrained to maintain correct solder height and prevent substrate collapse or unconnected solder joints.